PROJECT SUMMARY/ ABSTRACT Alzheimer?s disease (AD) is the fifth-leading cause of death for those age 65 and older and imposes substantial burden on patients, caregivers, and the health care system. It is critical to detect the cognitive decline and transition to mild cognitive impairment (MCI) when early interventions and treatments against AD could be most effective, and identify malleable risk factors in order to develop tailored preventive interventions. Recent evidence suggests that social relationships may play a dual role as risk factors for cognitive decline and MCI as well as indicators of these cognitive changes. However, most prior studies have relied on global assessments of social relationships at a single time point and thus are unable to examine temporal ordering in change in social relationships and cognitive function. The overall goal of this project is to use ?real time? ecological momentary assessments (EMAs) in naturalistic settings to better capture changes in daily social interactions--the manifestation of social relationships in daily life--associated with cognitive decline, disentangle the function of social interactions as indicators vs. risk factors for cognitive decline, and identify specific features of daily social interactions (frequency, diversity in types of partners, quality) that best prospectively predict short- and long-term cognitive decline. The proposed project will use data from a sample of 600 older adults enrolled in the well-established Einstein Aging Study Program Project (EAS) to link daily social interactions with cognitive function across different timescales ranging from days to years. Participants complete 4 annual 14-day EMAs of social interactions and cognitive performance 5 times per day (a measurement burst design), as well as annual clinic-based cognitive assessments and global social relationships surveys. Aim 1 will examine whether changes in daily social interactions indicate cognitive decline and impairment by testing whether individuals with vs. without MCI exhibit different patterns of daily social interactions, cross-sectionally and longitudinally. Aim 2 will examine short-term and long-term predictive effects of daily social interactions on cognitive decline and impairment. The approach is innovative in its use of intensive longitudinal assessments of both daily social interactions and cognitive function and analytic approaches that examine the temporal associations between daily social interactions and cognitive performance across different timescales. This project is significant because it will improve our understanding of dynamic associations between daily social interactions and cognitive function prior to the onset of AD. This knowledge will facilitate identification of specific features of daily social interactions as indicators or risk factors for cognitive decline and impairment, assisting in the early detection of the transition to MCI and development of intervention programs targeting specific features of daily social interactions as risk factors.